The present disclosure relates generally to information handling systems, and more particularly to a differential trace pair system used in an information handling system.
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Information handling systems such as, for example, switches, servers, and/or other computing devices typically include circuit boards with communication traces that are connected to different subsystems in order to provide for the transmission of information between those subsystems. For example, a differential trace pair may be provided between a transmitter subsystem and a receiver subsystem in the switch or server (or between different switches and/or servers) in order allow those subsystems to transmit and receive information. In some situations, the differential trace pair may couple to the transmitter subsystem and/or the receiver subsystem at connectors such as, for example, a pin included in a pin field (e.g., a Ball Grid Array (BGA) pin field.) The routing of differential trace pairs through such connectors can cause issues with the differential trace pair due to the connector arrangement, the placement of the differential trace pair, the angle of routing, and/or other differential trace pair routing characteristics known in the art. One of the common issues encountered in routing differential trace pairs in these and similar situations is when that routing results in one of the traces in the differential trace pair being longer than the other. This mismatch of trace length may cause common mode noise where a signal sent from the transmitter subsystem on the shorter trace in the differential trace pair arrives at the receiver subsystem before the signal that was sent from the transmitter subsystem on the longer trace in the differential trace pair. This problem is amplified as signal speeds increase beyond 25 Gbps, as the resulting common mode noise cannot be ignored, and issues associated with increased insertion and return loss are introduced.
Conventional systems attempt to remedy this issue by flipping the polarity at the receiver subsystem end of the differential trace pair such that the shorter trace leaving the transmitter subsystem end of the differential trace pair becomes the longer trace entering the receiver subsystem end of the differential trace pair. However, such solutions result in common mode noise throughout the routing of the differential trace pair, and are not possible on all system designs. Another conventional method for compensating for such differing trace lengths is to provide a serpentine trace region in the shorter trace that increases the length of the shorter trace to match that of the longer trace. The serpentine region length matching of the traces in the differential trace pair solves the common mode noise issue discussed above, but as signal speeds are increased to over 25 Gbps (e.g., 32 Gbps to 50/56 Gbps and beyond), the serpentine region length matching approach produces signal integrity issues. For example, when the shorter trace moves away from the longer trace in the serpentine region of the differential trace pair, an increase in impedance can occur (e.g., increases in impedance of 7-15 ohms have been observed depending on the stack-up cross-section and the material of the circuit board), resulting in high signal speed reflections and losses. Furthermore, in “tightly packed” printed circuit boards, the serpentine trace region may decrease the distance between the trace with the serpentine region and an adjacent single trace, or a trace of an adjacent differential trace pair, such that crosstalk coupling between the trace with the serpentine region and the adjacent trace may occur. Crosstalk is a phenomenon in which signal integrity is compromised when adjacent differential trace pairs are switching and noise from one differential trace pair couples to an adjacent differential trace pair or single trace.
Accordingly, it would be desirable to provide differential trace pairs with improved crosstalk performance.